In recent years, a storage system using a plurality of storage devices, such as an HDD (Hard Disk Drive), is widely used. In such a storage system, in general, the safety of data to be recorded is improved by performing recording control so that data is redundantly recorded in two or more storage devices using the RAID (Redundant Arrays of Inexpensive Disks) technique.
Further, in a storage system in which data is made redundant, if the use of one storage device is stopped due to a failure etc., the data stored in the storage device the use of which is stopped is rebuilt and stored in another storage device. Such processing is called “rebuild processing” generally. In many storage systems, a spare storage device called a hot spare is provided and the rebuild processing is performed using the hot spare in many cases. When a storage device fails, by performing the rebuild processing immediately using a hot spare as a data storage destination, it is possible to return a state to the state where data is made redundant in a brief time and to recover the safety of data in a brief time.
As a technique to recover the safety of data using a spare storage device, for example, there is a method in which a storage device having a high possibility of the occurrence of a failure is estimated based on the number of times of occurrence of an error and the data of the storage device is copied in advance in the spare storage device.
Further, as an example of control when a failure has occurred in a storage device, there is a system that performs control so that failure recovery processing is performed preferentially over the normal read and write processing when there is no margin in the degree of redundancy when a failure has occurred in a storage device. For example, the following literature describes such conventional methods and systems.
Japanese Laid-open Patent Publication No. 2010-128773
Japanese Laid-open Patent Publication No. 2005-100259
Japanese Laid-open Patent Publication No. 05-314674
In the rebuild processing, data is read from at least one of the remaining storage devices the use of which is continued and the data is written to another storage device. Because of this, while the rebuild processing is being performed, the burden of access processing in the remaining storage devices the use of which is continued and the burden of processing of a control device configured to control access to the storage device become heavy, and therefore, there is a possibility that the speed of data access in response to a request from a host device is reduced.
As described above, when the use of a storage device is stopped in the state where data is made redundant, it is possible to recover the redundancy of the data in a brief time by performing the rebuild processing as soon as possible. However, if the rebuild processing is performed in a brief time after the use of a storage device is stopped, there is a possibility that the speed of data access in response to a request from a host device is reduced during a predetermined period after the use of a storage device is stopped.